The present invention relates to systems and methods for generating ultrasound images, and more particularly to systems and methods for generating ultrasound images without system contact to the patient, which may be achieved, for example, using photoacoustic energy and/or laser vibrometry, in a manner that is safer for the eyes and skin.
Acoustic energy is used in numerous applications to characterize discontinuities, defects, and other mechanical properties within various types of materials. Acoustically-based techniques rely on differences in mechanical properties between a feature of interest and its local surroundings. These differences result in different vibrational responses to sonic excitation, which may be detected and the feature thereby localized and/or characterized.
An important advantage of acoustic techniques is the ability to detect discontinuities corresponding to (or indicating the presence of) flaws or hidden items that may not be detectable using visual or other techniques. Such discontinuities may represent latent defects that can compromise the mechanical integrity of load-bearing structures. Coupling a sufficient amount of acoustic energy into the medium of interest is critical, and in many cases it is the factor most limiting the efficacy of the technique. The large impedance mismatch between the ambient air and most solids or liquids makes the transfer of acoustic energy into the medium a generally inefficient process. Loudspeakers are omnidirectional thus suffering significant losses at large ranges. Parametric acoustic array (PAA) sources can provide directionality, but are limited to ranges on the order of tens of meters. An efficient means of coupling acoustic energy into media could have wide ranging benefits.
Ultrasonic imaging of the internal details of the human body can provide advantages relative to other techniques such as X rays (soft tissue contrast) and MRIs (faster and less cumbersome data acquisition). Typically, ultrasonic imagery is obtained in a “contact” manner in which an ultrasonic transducer (which both sends and receives the acoustic signals) is placed directly on (i.e., in contact with) the area of interest. Because of the very large acoustic impedance mismatch between air and the human body (acoustic coupling efficiency is only about 10−3), a coupling gel is generally used at the interface between transducer and tissue to increase coupling efficiency into the body. A range of contact ultrasound techniques exist. In general, an acoustic pulse is emitted into to the body. Echoes from structures are reflected back to the transducer, with the time of arrival giving information about the range to the structure. In a simple but fairly standard incarnation, the acoustic source is omnidirectional, thus only range information is obtained. A two-dimensional image is formed by using a line of transducers, which yield information in the cross range direction.
In certain circumstances, noncontact operation is highly desirable. If used in conjunction with a remote array source, it has the potential to mitigate the problems mentioned above related to 2D arrays. Additionally, there exist surgical situations in which sterility is an issue, situations in which contact is unpleasant or painful (such as imaging the eye), or emergency situations in which the patient is in transit and/or being stabilized and may not be easily imaged via a contact system. In certain triage situations it may be desirable to image multiple patients in as rapid a manner as possible, and a noncontact system may be able to provide this capability. Additional applications include, real-time surgical feedback imaging, traumatic brain injury (TBI) detection, bone health monitoring, and others. For example, real-time surgical guidance and feedback would greatly improve from an imaging technique that can directly access exposed skin or traumatized tissue without contact, especially in very delicate procedures such as spinal and neck surgery. Using a laser system eliminates couple gels (used in conventional ultrasound) applied on skin that can contaminate open body tissues. In addition, a laser system can provide fine spatial and temporal resolution to yield high quality images while reducing distortion observed with contact sensing deformation. Other benefits of such a system minimize patient discomfort over injured areas and setup times to acquire images, and are unlikely to interfere with other methods such as MRI, CT scan, fluoroscope, etc. A portable, lightweight non-contact ultrasonic vibration imaging device can provide very significant advantages over traditional ultrasonic contact devices. Ideally, a low power handheld laser imaging system can be used not only in a hospital setting, but would provide tremendous benefits in field operations. However, existing photoacoustic systems are limited in applicability due to safety concerns, as the lasers used in such systems could be harmful to patients, causing damage to, for example, the skin and eyes of patients.
Thus, there is a need for systems and methods capable of providing an efficient means for coupling acoustic energy into media in a noncontact manner to generate ultrasound images in a manner that does not pose an unacceptable risk of damage to patients, and in particular, to the eyes and skin of patients.